It is generally known to subject hard disks to a test prior to marketing them, during which test a test pattern is recorded on the medium which is then read out, after which the pattern read is compared with the original test pattern. The comparison yields information about the locations in the medium where media defects occur and also about the bit error rate. A media defect is present when information read from a particular location on the medium always results in an error. In contrast, normal read errors occur randomly and are not dependent on the location on the medium from which the information is read.
This known method, for which usually the address is to be administered for each bit location and checks are to be made whether the respective bit location has been correctly written and read out, lays a large claim on hardware and software and, moreover, requires much time especially where measuring the bit error rate is concerned. Such a laborious test is not attractive, particularly for the media customary nowadays which have large storage capacities, and for the fast delivery required by the customers and the large demand for hard disks.